computer keeps getting viruses that try to sell me anit virus software... and when I do not buy the soft ware the computer crashes and will not allow me to re-enter any of program.

I have had my computer serviced and they could not find any problems. When I went back on my e-mail accounts... it was then, that the computer did the exact same thing!! It comes up as "System Tools" and tells me that I have 38 viruses... which the Computer Tech confirmed that there was NOT any viruses in the computer.
Two hotmail accounts have been affected and now 2 computers are down because of this. [email protected]

please advise...